This invention relates to a method and apparatus for removing vapors and aerosols from gases produced by a high temperature gasification process, particularly such as a process to gasify solid fuels. More particularly, the present invention is addressed to the removal of harmful substances in the form of vapors or aerosols from the gases liberated by such a process at a location which is downstream of a gasification chamber and the return of such vapors or aerosols to undergo processing in the gasification chamber.
When finely-divided solid fuel is gasified, for example, at a high temperature in a slag bath generator, the fuel is injected together with a gasifying medium in the form of, for example, oxygen, steam or CO.sub.2, by a set of nozzles into a melting chamber of the generator. During such a process, the bottom of the melting chamber is covered with a liquid slag bath formed from the mineral constituents of the fuel. The resulting gases liberated during the process consist chiefly of carbon monoxide and hydrogen. These gases are cooled by injecting cold gases into the top of the gasifier chamber whereby the liberated gases are drawn off from the chamber at a temperature within the range of 800.degree. C. to 1000.degree. C.
As is known, these gases have been conducted into a dust collector in which most of the entrained solid particles are separated and deposited in the collector. The gases were then conveyed into a waste heat boiler where they are cooled down to about 250.degree. C. before the gases are fed into gas scrubbers and coolers located downstream of the waste heat boiler. The solid particles deposited in the dust collector consist mainly of flue coke; that is, pulverulent high temperature coke which is recycled into the reactor for gasification. The amount of coke recovered in the dust collector lies between 10% and 20% of the fuel used in the gasification chamber. During this high temperature gasification process, a number of lower boiling point chemical compounds is produced and evaporate, particularly when solid fuels such as coal are gasified under reducing conditions above the melting point of the mineral constituents of the coal.
The presence of lower boiling point chemical compounds depends, of course, upon the composition of the mineral substances in the coal which is used. However, these compounds are generally in the form of oxides, sulfides, sulfates and chlorides of silicon, potassium, calcium, sodium, magnesium, aluminum, iron and phosphorus. Thus, for example, the following compounds can be detected in gasified products: SiS, SiS.sub.2, SiO, K.sub.2 O and Na.sub.2 O. See, for example. W. Gumz et al, Schlackenkunde, Springer 1958. In addition, compounds such as NaCl, Na.sub.2 SO.sub.4, Na.sub.2 S.sub.2 O.sub.7, Na.sub.2 S, KCl, K.sub.2 SO.sub.4, K.sub.2 S.sub.2 O.sub.7, K.sub.2 S.sub.5, CaCl, CaS, CaSO.sub.4, MgSO.sub.4, Fe.sub.2 (SO.sub.4).sub.3, FeS, FeS.sub.2, Al.sub.2 (SO.sub.4).sub.3, Al.sub.2 S.sub.3, P.sub.4 S.sub.10 and P.sub.4 S.sub.3 may occur in the form of vapors or aerosols. These compounds are detectable in the gas stream when corresponding constituents are present in the minerals contained in the charging materials. These substances may also evaporate from the solid minerals present in the gas stream depending upon the partial pressure of the substances.
With regard to the aforementioned compounds which are soluble in water, such compounds are usually washed out of the gas by scrubbers located downstream of the gasification chamber. As a result, contamination of additional waste water and the environment occurs. With regard to those compounds which are not soluble in the washing solutions used in scrubbers or the like, these compounds either remain in the gas stream, i.e., reappear in the end product or, if the compounds in the gas reach a suitably low temperature, the compounds are deposited in the pipes, packed columns, valves, pumps, etc. in the gas purification plant. This, of course, produces premature stoppages and breakdowns of the purification plant or system.